First published Winter 2018


Last year, researchers questioned whether current public health advice to take vitamin D supplements during the winter needed to change. We look at recent research findings


In 2016, we were all advised to supplement vitamin D during the winter. Previously, it was only ‘at risk’ individuals — those who didn’t get much sunshine, or with dark skin, or who covered up when outside — who had been advised to take supplements. This had followed the report Vitamin D and Health by The Scientific Advisory Committee on Nutrition (SACN), which stated that from October to April, everybody should have an average daily intake of 10 micrograms of vitamin D (10 μg/d or 400 IU/d) to protect bone and muscle health, with at risk individuals advised to supplement all year round.

Vitamin D is essential for regulating calcium and phosphorus metabolism, both considered important for bone health. Severe deficiency can result in rickets in children, and osteomalacia in adults. Low levels are also associated with chronic diseases such as rheumatoid arthritis, multiple sclerosis, cardiovascular disease and diabetes — although it is unknown whether deficiency actually contributes to causing such conditions, which is why the 2016 SACN recommendations were only in relation to bone health.   

More recently, however, new research has raised questions of whether — or how — we should be supplementing. 

Bone health

Recently, a large study published in The Lancet Diabetes and Endocrinology, concluded that vitamin D supplements make no difference to the risk of bone fractures. The findings resulted from a large meta-analysis of 81 trials into vitamin D and bone health, with the authors stating: “Our findings suggest that vitamin D supplementation does not prevent fractures or falls, or have clinically meaningful effects on bone mineral density. There were no differences between the effects of higher and lower doses of vitamin D. There is little justification to use vitamin D supplements to maintain or improve musculoskeletal health. This conclusion should be reflected in clinical guidelines.”1

Some experts, however, argue that although the study combined over 80 studies to get a “bigger picture”, it did not look at people who were vitamin D-deficient.

Martin Hewison, a professor of molecular endocrinology at the University of Birmingham, said: “The vast majority of the people in these studies were not actually vitamin D-deficient and thus the authors were always unlikely to see much of an effect.”

There are also suggestions that vitamin D should be studied in conjunction with magnesium, which may have an effect on vitamin D’s efficacy. However, the lead author of The Lancet study, Dr Mark Bolland, PhD, told Optimum Nutrition: “Proponents of combined magnesium and vitamin D should study the combination in clinical trials before making clinical claims about the efficacy of such supplements. I think trials have been done with bone density as an outcome, and showed that adding vitamin K or multivitamins to vitamin D and/or calcium did not have any effect.” However, a recent randomised trial has found that magnesium does appear to regulate how we synthesise vitamin D.

Magnesium and vitamin D

Since we spoke to Dr Bolland, however, a randomised trial involving 250 people has found that magnesium appears to optimise and regulate vitamin D levels.2

A team at the Vanderbilt-Ingram Cancer Center, USA, were interested in the role of magnesium after it was observed that people synthesise vitamin D differently, with levels not rising in some people even after being given a high dose.

Lead author Qi Dai, MD, PhD, Ingram Professor of Cancer Research, said that magnesium deficiency “shuts down” the pathway for vitamin D to be synthesised and metabolised.

Last year, a separate review also concluded that vitamin D needed magnesium to be metabolised; otherwise it remains stored and inactive. Mohammed Razzaque, MBBS, PhD, a professor of pathology at Lake Erie College of Osteopathic Medicine, said: “People are taking vitamin D supplements but don’t realise how it gets metabolised. Without magnesium, vitamin D is not really useful or safe.”

(Magnesium can be supplemented by adding Epsom salts to a hot bath.)

Obesity and children

The European Society for Paediatric Endocrinology has reported that vitamin D supplements may promote weight-loss and reduce risk factors for heart and metabolic disease in overweight and obese children.

Researchers from the University of Athens Medical School and the Aghia Sophia Children’s Hospital in Athens had assessed 232 obese children and adolescents, randomly assigning 117 to receive vitamin D supplementation. After a year, it was found that children who had been given vitamin D supplements had significantly lower body mass index, body fat, and improved cholesterol levels.

However, the authors cautioned that although the findings may indicate that vitamin D could be used in the treatment of obesity, there was a lack of evidence on the safety and long-term effects of supplementation — particularly when there was no initial vitamin D deficiency. In the case that a child was overweight or obese, they advised consulting a primary care physician for advice, and to consider having the child’s vitamin D levels tested.4

INFANT Vitamin D deficiency

In June 2018, researchers from the University of Birmingham called for a revision of public health recommendations for vitamin D, after the death of a six-month-old baby following complications of heart failure, and serious illness in two other babies. The six-month-old, who was of Somalian descent, had low calcium, severe heart failure and rickets due to severe vitamin D deficiency.

Dr Wolfgang Högler, a reader in paediatric endocrinology at the University of Birmingham’s Institute of Metabolism and Systems Research and a consultant endocrinologist at Birmingham Children’s Hospital, and Dr Suma Uday, a PhD doctoral researcher, argued that recommendations for infants and children were overly complex and outdated. They called for all babies — whether formula- or breast-fed — to be given vitamin D from birth. Currently it is only recommended that breast-fed babies are given vitamin D supplements, because formula is fortified with vitamin D.

Högler and Uday also called for mandatory monitoring of babies and pregnant women, to ensure vitamin D supplements were being taken. They outlined cases of three babies born in England to mothers of Black, Asian and Minority Ethnic origin. All three babies had developed low-calcium heart failure and rickets. It was also found that five family members of the three babies also had bone disease caused by vitamin D deficiency.5 The study concluded: “The family investigations demonstrate widespread deficiency and undiagnosed osteomalacia in ethnic risk groups and call for protective legislation.”

How supplements are made

Keeley Berry, nutritional expert and new product development executive at BetterYou Ltd, explains the difference between vitamins D2 and D3, and how they are made.

“There are two main forms of vitamin D which are ergocalciferol (D2), which comes from plant sources and fortified foods, and cholecalciferol (D3) that is mostly found in animal-sourced foods.

“Most D3 cholecalciferol supplements are sourced from lanolin in sheep wool or lichen. Sheep wool undergoes extraction processes to produce cholesterol, which can be converted into 7-dehydrocholesterol — known as pre-vitamin D3. This product is then irradiated to produce cholecalciferol, which is the same reaction that happens in human skin when producing vitamin D from sunlight.

“Lichen are small algae-like plants that have been exposed to UV rays, however quantities of vitamin D3 that are extracted from the plants are much lower in comparison to lanolin sources.

“Other plant sources such as mushrooms produced under UV light make the D2 form of the vitamin, which is then extracted and used for supplements or fortification of dairy-free milks and cereals.

“However, vitamin D2 and D3 are not equal when it comes to raising vitamin D levels as the liver metabolises them differently. Both forms of the vitamin convert into calcifediol in the liver (also known as calcidiol), however, D2 yields less calcifediol than D3, making it inferior when it comes to raising blood levels.”

Food sources of vitamin D include oily fish, some mushrooms, and fortified food.



Read more articles and recipes  



  2. Vanderbilt University Medical Center. Study shows magnesium optimizes vitamin D status.
  4. Vitamin D supplements may promote weight loss in obese children.